The ExtractionâFlocculation Re-refining Lubricating Oil Process

3854

Ind. Eng. Chem. Res. 1997, 36, 3854-3858

GENERAL RESEARCH The Extraction-Flocculation Re-refining Lubricating Oil Process Using Ternary Organic Solvents J. P. Martins Departamento de Engenharia Quı´mica, Laborato´ rio de Cata´ lise e Materiais, FEUP, Rua dos Bragas, 4099 Porto Codex, Portugal

Waste lubricating oils may be re-refined with organic solvents that dissolve base oil and segregate the additives and solid particles. The present paper emphasizes the composition effect on the efficiency of a ternary solvent composed by n-hexane/2-propanol/1-butanol. Using the ternary diagram of waste oil/basic organic component/polar compound containing 3 g/L KOH where the phase envelope and the curves of constant sludge removal are plotted, it is proposed the composition of 0.25 waste oil/0.35 n-hexane/0.40 polar compound (80% 2-propanol + 20% 1-butanol, with 3 g/L KOH) for the process. A contribution for the understanding of polymethacrylate flocculation supported on infrared spectra is given. Introduction The disposal of waste lubricating oils in landfills and/ or city sewers can be disastrous due to the possible contamination of soils and waterways. Hopmans (1974) estimated that the discharge of spent oil is equivalent to the diary rejects in a 40 000 people urban sewer. The acid-clay technology was one of the most commonly used lube oil recovery process. Beyond the yields of base oils, the corrosion problems, and the maintenance costs, the main disadvantage of this process is related to the application of the acid tar and of the spent clay. Berry et al. (1977) proposed the introduction of the spent clay in Portland cement kilns. Acid sludge disposal problems are the main incentive for the development of processes based on the extraction-flocculation properties of organic solvents. Consequently, alternatives based on this approach were studied in the past; some of the solvents suggested were, for example, 1-butanol by Brownawell and Renard (1972), butanone by Jordan and McDonald (1973), a solution of 1-butanol/2-propanol/butanone by Whisman et al. (1978a,b) and a solution of n-hexane/2-propanol with 3 g/L KOH by Reis (1982). Pilot plant tests have been done by Corlew and Sluski (1976) with the solvent proposed by Whisman and by Reis (1991) using his own solvent. Detailed economical analysis of both these alternative processes conduced by Bigda et al. (1977a) and CREFOL (1984), respectively, show that processing costs of 37.9 cents/gal result, i.e., about 20% less than the cost of the classic acid/clay technology (Bigda et al., 1977b). The organic sludges obtained with polar solvents may be incorporated in asphalts or, better, used as a component of offset inks (Reis and Jeronimo, 1982). More recently, the Mohawk-CEP process for rerefining of lubricating oils has been implanted in North America (Magnabosco et al., 1991). This is considered the newest and higher-efficiency re-refining technology developed so far. The key steps involve the allimportant Mohawk treatment and the base oil recovery via thin-film vacuum distillation that produces base lube oils in the overhead product and asphalt in the bottoms. The deleterious metals wind up encapsulated in the S0888-5885(96)00593-3 CCC: $14.00

asphalt fraction that meets the leaching test criteria. So, the asphalt produced can be used as a blending component for the road paving asphalt or for the production of roofing shingles. The raw base lube oils from the distillation are catalytically converted (Magnabosco, 1990) to improve color and stability. For a plant capacity of 8 million gallons per year, the total cost plant investment amounts to about $10 million with processing costs of 42.5 cents/gal. In this work, the principles of extraction-flocculation solvent and the method to formulate efficient composite solvents by Reis and Jeronimo (1988,1990) are applied to find the best composition of a ternary solvent of n-hexane/2-propanol/1-butanol. Also, the insight on the polymethacrylate flocculation is improved by using infrared spectra. Polymers Solubility in Organic Solvents The solubilization mechanism of polymers in organic solvents is more complex than that in aqueous systems; several works like the ones of Ueberreiter et al. (1962), Asmussen et al. (1962), Hildebrandt and Scott (1964), Hoy (1970), Hildebrandt et al. (1970), Krevelen (1976), Elias (1977), etc., address this subject. Since the dissolution of a polymer is always connected with an entropy increase, the spontaneity of the process will be dependent on the heat of the mixing. This heat of mixing per unit volume can be approximated (Hildebrandt, 1964) by

∆H ) v1v2(δ1 - δ2)2

(1)

where v is the volume fraction, δ the solubility parameter, and subscripts 1 and 2 refer to solvent and polymer, respectively. Table 1 from Burrell (1975) shows the influence of the solvent (measured by the H-bond energies) on the solubility parameter for some polymers. As a first approximation and in the absence of strong interactions, polymer solubility is expected if (δ1 - δ2) is less than 3.5-4.0 (Billmeyer, 1984) but not if it is appreciably larger. Considering Burrell data (cf. Table 1), the solubility of the polyolefins and polymethacrylates or other nonpolar compounds is possible © 1997 American Chemical Society

Ind. Eng. Chem. Res., Vol. 36, No. 9, 1997 3855 Table 1. Solubility Parameter Ranges of Some Polymers solubility parameter in hydrogen bond solvent [J/m3]1/2 × 103 polymer

poorly

moderately

strongly

poly(butyl methacrylate) poly(ethyl methacrylate) poly(methyl methacrylate) poly(hexyl methacrylate) poly(lauryl methacrylate) poly(octyl methacrylate) poly(propyl methacrylate) poly(methacrylic acid) poly(isobutylene)

14.3-26.0 17.4-22.4 18.2-26.0 17.6 16.6 17.2 18.0 0 16.2

15.1-24.8 16.0-27.2 17.4-27.2

19.4-26.0 19.4-23.3 0

20.3

26.0-29.7

in lube oil. If an organic solvent composed of a nonpolar (n-hexane) and a polar compound (2-propanol and or 1-butanol) is added to this solution, the polyolefins (as polyisobutylene) are segregated while some polymethacrylates are maintained in solution. The tests performed by Reis and Jeronimo (1988) on waste oil or synthetic dispersions showed that the carbonaceous particles remain in a stable dispersion if there is no segregation of polymer molecules. They attributed this behavior to the polar nature of the alcohol and suggested the introduction of KOH to break the stability by neutralizing the exceeding charges in the solution. Particle instabilization is controlled by the chemical and electrical parameters of the system. The flocculation of charged particles can occur by two mechanisms: (1) reduction of the electrostatic repulsion between particles and (2) formation of bridges between particles. Using KOH inside the organic solvent we think that the carbonaceous or similar particles follow the first mechanism, while polymethacrylates are instabilized by the second after the following chemical reaction, – O

O –CH2C(CH3)

C

OR +

OH–

–CH2(CH3)

C

OR

OH O –CH2C(CH3)

C

OH + RO–

(2)

Taking into account eq 1 or/and the data of Fuchs and Suhr (1975), it is reasonable to confirm the segregation of polymethacrylates as a result of the poly(methacrylic acid) production by the chemical reaction referred to above. Experimental Section The base oil SAE-20 was supplied by Petrogal and the waste oil reported as MWO is a mixture of ten 2-L samples collected from 200-L drums at ten different service stations. The organic compounds were reagent grade. The monophasic and biphasic regions of the ternary diagram base oil/hydrocarbon/polar compound were performed in a thermostatic medium. The experimental procedure for the determination of the phase envelope was as follows: Weighed amounts of SAE-20 and polar compound were brought into a test tube; then the hydrocarbon was added until a clear solution was obtained. The limiting points of the phase envelope (in the absence of n-hexane) were determined by adding the polar compound to a weighed amount of SAE-20 until a persistent turbidity was observed. The percent sludge

Figure 1. Infrared spectrum of Plexol 702 SP (20%) in SAE-20.

Figure 2. Infrared spectrum of sludges from the treatment of the dispersion of Plexol 702 SP (20%) in SAE-20 with the organic solvent (0.45 n-hexane + 0.44 2-propanol + 0.11 1-butanol, with 3 g/L KOH).

removal was obtained according to the method described by Reis and Jeronimo (1988). Settling curves were performed and the sludges microscopically analyzed. In what follows, all compositions are expressed in weight fractions. After the decision about the best organic composition the waste oil was treated to analyze some properties of the intermediate and finished oil. First a distillation (T ) 160 °C; P ) 5 mmHg) of the waste oil was performed in order to remove the light hydrocarbons and water, then an extraction-flocculation process to remove the sludges followed by a distillation of the oil (T ) 150 °C; P ) 10 mmHg) to remove the solvent was done, and finally a clay treatment (T ) 150 °C; P ) 760 mmHg; t ) 1 h) or a percolation through a bauxite bed (T ) 70 °C) to improve the quality of the finished oil was performed. Infrared spectra were obtained to investigate the action of potassium hydroxide on polymethacrylates and to analyze the possibility of using the sludges in asphaltic ink. Two infrared analyses were performed: one on a 20% solution of a pure additive (Rohm and Haas Plexol 702 SP) for multigrade oils in SAE-20 base oil and another on the sludges from the treatment of the previous solution with the organic solvent (0.45 n-hexane + 0.44 2-propanol + 0.11 1-butanol, with 3 g/L KOH). The last spectrum was compared with the infrared spectrum of a standard bituminous ink. Results and Discussion Infrared spectra in Figures 1 and 2 support the assertion that the segregation of polymethacrylate is related with the formation of poly(methacrylic acid). As a matter of fact, a strong absorption band of the carbonyl group peaks at 1740 cm-1 together with the typical band for stretching in esters at 1240 cm-1 can be seen in Figure 1, before the organic solvent treatment. After the treatment (Figure 2) while the carbonyl peak at 1740 cm-1 remains visible, the ester band at low wavenumbers is removed. However, a new band appears in the 3500-3100 cm-1 range characteristic of the OH stretch n-carboxylic acids.

3856 Ind. Eng. Chem. Res., Vol. 36, No. 9, 1997

Figure 3. Ternary diagram for the system oil/n-hexane/polar compound (60% 2-propanol + 40% 1-butanol, with 3 g/L KOH).




Figures 3-6 show the phase envelopes for the system SAE-20/n-hexane/polar compound with 3 g/L KOH at 25 °C and different ratios of 2-propanol to 1-butanol. The solid lines are the geometric sites of compositions corresponding to constant solvent to oil weight ratios (R). The sludge removal results for the range of compositions between the weight ratios R ) 2 and R ) 8 are also plotted. When the amount of 2-propanol changes from 60% to 90% in the polar compound, there is an enlargement in the phase envelope. The sludge removal also increases with the ratio R, which conforms to the action of the extracting organic solvent. From the curves of constant percentage sludge removal, the importance of the polar compound (2-propanol + 1-butanol with 3 g/L KOH) on the organic solvent composition is shown. Table 2 shows the polar compound/waste oil + n-hexane ratios for constant sludge removal as a

function of the polar compound composition and solvent/ waste oil ratio R. Microscopic analyses show an increase of the flake dimensions and sludges compactness with the amount of 1-butanol. An increase in the settling rate with the amount of 1-butanol was also observed. To choose the ideal solvent composition, the following rules were taken into account: the lower solvent/waste oil ratio and the lower polar compound/waste oil + n-hexane ratio, the better the settling rate and the lower polar compound cost. The best result corresponds to an 80% 2-propanol + 20% 1-butanol composition of the polar compound. Table 3 summarizes some properties of the MWO, intermediate oil, and finished oil. The results show that re-refined oils have good physical and chemical properties (similar to common values of virgin oils). A better

Ind. Eng. Chem. Res., Vol. 36, No. 9, 1997 3857 Table 2. Values Corresponding to Polar Compound/ Waste Oil + n-Hexane Ratios for Equal Sludge Removal sludge removal

% 2-propanola

R

6%

9%

12%

60 60 60 60 70 70 70 70 80 80 80 80 90 90 90 90

2 4 6 8 2 4 6 8 2 4 6 8 2 4 6 8

0.500 0.579 0.695 0.724 0.494 0.558 0.681 0.691 0.376 0.498 0.568 0.701 0.465 0.565 0.535 0.759

0.690 1.028 1.089 1.219 0.632 0.940 1.062 0.932 0.526 0.849 0.744 0.894 0.721 0.953 0.783 0.985

0.880 1.478 1.485 1.969

a

15%

1.880

1.323 1.443 1.201

1.823 1.509

1.199 0.920 1.103

1.095 1.332

1.342 1.056 1.237

1.361 1.529

Percentage of 2-propanol in the polar compound.

finished oil

color1 specific gravity2 viscosity (40 °C), cSt3 viscosity (100 °C), cSt3 viscosity index4 TAN5 TBN6 metals, ppm7 Ca Zn Mg Fe Pb

Acknowledgment I wish to express my gratitude to Engs. Miranda and Costa Leme for their help in the experiments, and to Professors J. M. Loureiro, M. R. Costa, and Joaquim Faria for helpful discussions. This work was dedicated to Professor M. Alves dos Reis. Literature Cited

Table 3. Properties of Waste Oil and Intermediate and Finished Re-refined Oils, Viscosimetric Specificationa

properties

been reported in the form of a ternary diagram. Taking into account technical and economic aspects, the composition of 0.25 waste oil, 0.35 n-hexane, and 0.40 polar compound (80% 2-propanol + 20% 1-butanol with 3 g/L KOH) is proposed for the extraction-flocculation process in the re-refining of waste oils. The segregation of polymethacrylate is related with a nucleophilic substitution giving a poly(methacrylic acid). The waste oil sludges can be reclaimed under the form of asphaltic inks.

waste oil

pretreated oil

clay treatment

bauxite percolation

black 0.900 114.52

8 0.890 78.80

3 0.885 54.45

3 0.880 53.05

13.64

10.32

7.36

7.25

131 2.15 3.35

110 0.45 2.85

104 0.09 0

102 0.04 0

1800 1200 600 58 750

230 150 130 20 161

The ExtractionâFlocculation Re-refining Lubricating Oil Process

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